.\" -*- nroff -*-
.\" Copyright 2013 Los Alamos National Security, LLC. All rights reserved.
.\" Copyright 2010 Cisco Systems, Inc.  All rights reserved.
.\" Copyright 2006-2008 Sun Microsystems, Inc.
.\" Copyright (c) 1996 Thinking Machines Corporation
.\" Copyright 2015-2016 Research Organization for Information Science
.\"                     and Technology (RIST). All rights reserved.
.\" $COPYRIGHT$
.TH MPI_File_iwrite_at 3 "Jun 10, 2020" "4.0.4" "Open MPI"
.SH NAME
\fBMPI_File_iwrite_at\fP \- Writes a file at an explicitly specified offset (nonblocking, noncollective).

.SH SYNTAX
.ft R
.nf
.SH C Syntax
.nf
#include <mpi.h>
int MPI_File_iwrite_at(MPI_File \fIfh\fP, MPI_Offset \fIoffset\fP,
	const void \fI*buf\fP, int \fIcount\fP, MPI_Datatype \fIdatatype\fP, MPI_Request \fI*request\fP)

.fi
.SH INPUT/OUTPUT PARAMETER
.ft R
.TP 1i
fh
File handle (handle).

.SH INPUT PARAMETERS
.ft R
.TP 1i
offset
File offset (integer).
.ft R
.TP 1i
buf
Initial address of buffer (choice).
.ft R
.TP 1i
count
Number of elements in buffer (integer).
.ft R
.TP 1i
datatype
Data type of each buffer element (handle).

.SH OUTPUT PARAMETERS
.ft R
.TP 1i
request
Request object (handle).
.TP 1i
IERROR
Fortran only: Error status (integer).

.SH DESCRIPTION
.ft R
MPI_File_iwrite_at is a nonblocking version of MPI_File_write_at. It attempts to write into the file associated with
.I fh
(at the
.I offset
position) a total number of
.I count
data items having
.I datatype
type from the user's buffer
.I buf.
The offset is in
.I etype
units relative to the current view. That is, holes are not counted
when locating an offset. The data is written into those parts of the
file specified by the current view. MPI_File_iwrite_at stores the
number of
.I datatype
elements actually written in
.I status.
All other fields of
.I status
are undefined. The request structure can be passed to MPI_Wait or MPI_Test, which will return a status with the number of bytes actually accessed.
.sp
It is erroneous to call this function if MPI_MODE_SEQUENTIAL mode was specified when the file was open.

.SH FORTRAN 77 NOTES
.ft R
The MPI standard prescribes portable Fortran syntax for
the \fIOFFSET\fP argument only for Fortran 90.  FORTRAN 77
users may use the non-portable syntax
.sp
.nf
     INTEGER*MPI_OFFSET_KIND \fIOFFSET\fP
.fi
.sp
where MPI_OFFSET_KIND is a constant defined in mpif.h
and gives the length of the declared integer in bytes.

.SH ERRORS
Almost all MPI routines return an error value; C routines as the value of the function and Fortran routines in the last argument. C++ functions do not return errors. If the default error handler is set to MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception mechanism will be used to throw an MPI::Exception object.
.sp
Before the error value is returned, the current MPI error handler is
called. For MPI I/O function errors, the default error handler is set to MPI_ERRORS_RETURN. The error handler may be changed with MPI_File_set_errhandler; the predefined error handler MPI_ERRORS_ARE_FATAL may be used to make I/O errors fatal. Note that MPI does not guarantee that an MPI program can continue past an error.

